It has been known for several years that aircraft landing gear wheels or trains of wheels may be steerable in normal use by means of a double-acting hydraulic actuator. The actuator is disposed transversely to the post which contains a shaft having the wheel(s) disposed at its bottom end. The actuator comprises two opposing pistons interconnected by a common piston rod which has a toothed zone or rack in its middle, between the pistons. The rack meshes with a toothed sector fixed to rotate said shaft.
Because of its transverse disposition, the actuator can only be of limited length, such that the angular deflection of the toothed sector on the shaft which carries the wheels is limited to a value of less than .+-.90.degree. about the straight ahead position. This limited value is too small for moving the aircraft in a confined space, e.g. in a hangar. Under such circumstances it is often desirable to be able to swivel the wheel through a much greater angle than +90.degree..
A widely used conventional solution consists in providing a decoupling member, such as a pin, for example, between the toothed sector and the wheel, which member is removed by hand, thereby enabling the wheel to be swivelled independently of the actuator. A serious drawback of such means is that safety is compromised since the wheel can no longer be steered from the pilot position if the decoupling member is not replaced.
Preferred embodiments of the present invention provide improved steerable aircraft landing gear in which the steered wheel(s) may be declutched at will from the hydraulic steering actuator while including intrinsic safety in the sense that coupling between the actuator and wheel(s) is automatically reestablished whenever the wheel is manually returned to the range of angular deflection which is under actuator control.